In this case Object.ByGeometry will not work because the Dynamo object type (PolySurface) that you are trying to pass back to AutoCAD does not have a corresponding AutoCAD object to “convert” to. Dynamo works as a standalone application, so it has a lot of it’s own native geometry types. This doesn’t necessarily mean that all of those object types will map directly back to AutoCAD.
Following are the AutoCAD geometries that can be created from Dynamo geometries, to my knowledge. I won’t say that this list is exhaustive; I definitely could be missing something here. The formatting I’m using is [Dynamo object] -> [Node] -> [AutoCAD object]. Bold text means that the node is not available OOTB and is part of the Civil 3D Toolkit package.
Arc -> Arc.ByGeometry or Arc.ByThreePoints -> Arc
Circle -> Object.ByGeometry -> Circle
Face -> Face.ByGeometry -> 3D Face
Hatch -> Hatch.ByGeometry -> Hatch
Line -> Object.ByGeometry -> Line
Mesh -> Mesh.ByGeometry -> Polyface Mesh
Polyline -> PolylineExtensions.ObjectByGeometry -> Polyline
N/A -> Polyline3D.ByPoints -> 3D Polyline
Solid -> Object.ByGeometry -> 3D Solid
So back to your original question…I would try first creating the surface in Dynamo, perhaps using Curve.Extrude. From there, you could either use Topology.Faces -> Face.ByGeometry or try to convert the extruded surface to a mesh and then send that to CAD as a Polyface Mesh using Mesh.ByGeometry.